Implement Phase 9: Prometheus Metrics (v0.9.0)

- Add Prometheus metrics integration via wp-prometheus hooks
- Create Grafana dashboard JSON with 24 panels
- Add metrics settings tab with enable/disable toggle
- Expose inventory, booking, occupancy, revenue, and guest metrics

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

README.md

@@ -21,6 +21,7 @@ WP BnB Management enables WordPress to act as a full management system for B&B h
 - **Contact Form 7 Integration**: Accept booking requests and inquiries through CF7 forms
 - **Dashboard**: Comprehensive admin dashboard with statistics and charts
 - **Reports**: Detailed reports with CSV and PDF export
+- **Prometheus Metrics**: Expose operational metrics for monitoring with Grafana
 
 ### Requirements
 
@@ -383,6 +384,66 @@ add_action( 'wp_bnb_before_booking_create', function( $booking_data ) {
 } );
 ```
 
+## Prometheus Metrics
+
+The plugin integrates with [WP Prometheus](https://src.bundespruefstelle.ch/magdev/wp-prometheus) to expose operational metrics for monitoring with Prometheus and Grafana.
+
+### Enabling Metrics
+
+1. Install and activate the WP Prometheus plugin
+2. Navigate to **WP BnB → Settings → Metrics**
+3. Enable "Expose BnB metrics via Prometheus"
+4. Metrics will be available at your site's `/metrics/` endpoint
+
+### Available Metrics
+
+**Inventory Metrics:**
+
+- `wp_bnb_buildings_total` - Total number of buildings
+- `wp_bnb_rooms_total{status}` - Rooms by status (available, occupied, maintenance, inactive)
+- `wp_bnb_services_total{status}` - Services by status (active, inactive)
+- `wp_bnb_total_capacity_beds` - Total bed capacity across all rooms
+
+**Booking Metrics:**
+
+- `wp_bnb_bookings_total{status}` - Bookings by status (pending, confirmed, checked_in, checked_out, cancelled)
+- `wp_bnb_checkins_today` - Check-ins scheduled for today
+- `wp_bnb_checkouts_today` - Check-outs scheduled for today
+- `wp_bnb_bookings_upcoming_7days` - Bookings starting in next 7 days
+- `wp_bnb_booking_avg_duration_nights` - Average booking duration
+
+**Occupancy Metrics:**
+
+- `wp_bnb_occupancy_rate_current` - Current room occupancy rate (percentage)
+- `wp_bnb_occupancy_rate_this_month` - Monthly occupancy rate (percentage)
+- `wp_bnb_rooms_currently_occupied` - Rooms currently occupied
+
+**Revenue Metrics:**
+
+- `wp_bnb_revenue_this_month{currency}` - Revenue for current month
+- `wp_bnb_revenue_ytd{currency}` - Revenue year to date
+- `wp_bnb_booking_avg_value{currency}` - Average booking value
+- `wp_bnb_services_revenue_this_month{currency}` - Services revenue this month
+
+**Guest Metrics:**
+
+- `wp_bnb_guests_total` - Total registered guests
+- `wp_bnb_guests_by_status{status}` - Guests by status (active, blocked, vip)
+- `wp_bnb_guests_repeat` - Guests with more than one booking
+- `wp_bnb_guests_new_this_month` - New guests this month
+
+### Grafana Dashboard
+
+A pre-configured Grafana dashboard is included at `assets/grafana/wp-bnb-dashboard.json`. If WP Prometheus is installed, the dashboard is automatically registered and available for export.
+
+The dashboard includes:
+
+- Occupancy gauges with color-coded thresholds
+- Bookings, rooms, and guests pie charts by status
+- Revenue and guest statistics panels
+- Today's check-ins/check-outs
+- Trend indicators
+
 ## Frequently Asked Questions
 
 ### Do I need a license to use this plugin?